Dynamax HPFM3, Инструкция по установке и эксплуатации, Страница: 7 / 86

Revision: JUNE 2017 7
1.1 High Pressure Flow Meter (HPFM) Form & Function
The HPFM is shown schematically in Figure 1. It is an apparatus designed to perfuse water into an object while rapidly
changing the delivery pressure and simultaneously measuring flow. This is referred as a transient conductance
measurement. The slope of flow plotted versus pressure equals the hydraulic conductance of the object. The object
can be an excised shoot or excised root system or capillary tube (for test purposes). The HPFM may also measure quasi-steady
state conductance, i.e., under conditions where flow and applied pressure are approximately constant with time.
To measure a transient, a rapid change in water pressure is achieved using a pressure regulator (R), a needle valve
(NV), and a captive air tank (CAT). A pressure regulator (R) delivers compressed air from the compressed air tank (CAT).
The pressure regulator keeps the compressed air at a steady pressure of 4 to 5 MPa (580-725 PSI) through a needle valve
(NV).
The NV flows are in to the air-chamber (A) of a captive air tank (CAT). A rubber diaphragm separates the air
from water (W) in the CAT. The NV is adjusted to permit a rate of airflow to pressurize the air volume at a rate of
3 to 7 kPa s-1 (approx. 1-PSI s-1). The volumes of air and water are approximately equal in the CAT. The CAT can be
pressurized or depressurized by turning the 3-way ball valve (AV).
A pressure release valve (PR) prevents accidental over-pressurization. The pressure release valve is set to vent air when
the pressure exceeds about 0.6 MPa (87 PSI). Since the pressure in (A) never exceeds 0.6 MPa, and the air supply is
4.2 MPa (609 PSI), the pressure drop across the NV is approximately constant. This allows the rate of pressurization in
the water to be approximately linear with time.
Pressurized water flows from the CAT to the 8-Way Inlet manifold (8WI) through a 9 mm Inside Diameter (ID) nylon-
reinforced Tygon tubing. At a distance of 0.3 m from the CAT the water passes through a 0.1 micron water filter, then the
diameter of the tubing is reduced to 3 mm Outside Diameter (OD) plastic tube; the plastic tubing is connected to the input
side of the 8WI. The 8WI is shown schematically in Figure 1. The 8WI is an 8-Way HPLC valve of octagonal geometry with
8-tubes emerging from a common point in the center and each tube terminated by a valve.
On the inlet side, the 3 mm OD (1.5 mm ID) tube from the CAT is connected to one of the 8 valves (purple connector on
the HPFM). A pressure transducer (PT1) is connected to another valve (blue connector on the HPFM). On the outlet side
another pressure transducer (PT2) is connected to 8WI (blue connector) as well as the 3 mm OD (1.5mm ID) outlet tube
(purple connector). This leaves 6 pairs of valves available between each 8WI and 8-Way Outlet (8WO) for connection of
narrow-bore capillary tubes (CT).
The capillary tubes are 1.5 mm OD HPLC tubing 0.16 to 1.5 m in length. The HPLC CTs have internal diameters from 0.12
to 0.5 mm. During a measurement, one CT is selected by opening the inlet and outlet valves of the corresponding manifold
(8WI and 8WO). The corresponding CT valves for the unused capillary tubes must be closed. Water flow across the
selected CT causes a differential pressure (dP) drop (dP = P1 -P2) measured with PT1 and PT2, respectively.
Figure 1
Schematic of High Pressure Flow Meter (HPFM)
W
A
CT